[REF] tools: rename extras into tools

tools/benchmarks/shared/main.css

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+.main {
+  position: absolute;
+  left: 0;
+  right: 0;
+  top: 0;
+  bottom: 0;
+
+  display: grid;
+  grid-template-columns: 220px 1fr;
+}
+
+.left-thing {
+  background-color: gray;
+  padding: 20px;
+  color: white;
+}
+
+.left-thing button {
+  width: 100%;
+}
+
+.right-thing {
+  padding: 20px;
+  overflow: auto;
+}
+
+/* Message widget */
+.message .author {
+  font-weight: bold;
+}
+
+.message {
+  width: 400px;
+  background-color: lightblue;
+  margin: 10px 5px;
+  border-radius: 5px;
+  padding: 5px;
+}
+
+.remove {
+  float: right;
+}

tools/benchmarks/shared/utils.js

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+//------------------------------------------------------------------------------
+// Generating demo data
+//------------------------------------------------------------------------------
+const AUTHORS = ["Aaron", "David", "Vincent"];
+const CONTENT = [
+  "Lorem ipsum dolor sit amet",
+  "Sed ut perspiciatis unde omnis iste natus error sit voluptatem",
+  "Excepteur sint occaecat cupidatat non proident"
+];
+
+function chooseRandomly(array) {
+  const index = Math.floor(Math.random() * array.length);
+  return array[index];
+}
+
+let nextId = 1;
+export function buildData(n = 1000) {
+  const data = [];
+  for (let i = 0; i < n; i++) {
+      let id = nextId++;
+    data.push({
+      id: id,
+      author: chooseRandomly(AUTHORS),
+      msg: `${id}: ${chooseRandomly(CONTENT)}`,
+      likes: 0
+    });
+  }
+  return data;
+}
+
+//------------------------------------------------------------------------------
+// Measuring helpers
+//------------------------------------------------------------------------------
+let startTime;
+let lastMeasure;
+export function startMeasure(descr) {
+  startTime = performance.now();
+  lastMeasure = descr;
+}
+export function stopMeasure() {
+  let last = lastMeasure;
+  if (lastMeasure) {
+    window.setTimeout(function() {
+      lastMeasure = null;
+      const stop = performance.now();
+      console.log(`[${last}] took  ${Number(stop - startTime).toFixed()}ms`);
+    }, 0);
+  }
+}